1. Field of the Invention
The present invention relates to a multi-mode communication device which establishes a communication path through an application of appropriate communication control in response to a given multiplex-attachement scheme when the given multiplex-attachment scheme is selected from a plurality of multiplex-atachement schemes, inclusive of a code-division-multiplex-attachment scheme, to be employed in a radio-transmission path.
2. Description of the Related Art
Because of a recent development in electrical-power-transfer control, a code-division-multiplex-attachment scheme is now applicable to mobile-communication systems despite of the fact that lengths of radio-transmission paths and a propagation loss greatly vary in such systems. Hereinafter, code-division-multiplex-attachment scheme is referred to as a CDMA scheme.
Such mobile-communication system employing a CDMA scheme is less susceptible to interference and noise than are systems employing other multiplex attachment schemes such as a frequency-division-multiplex-attachment scheme (hereinafter, referred to as an FDMA scheme) and a time-division-multiplex-attachement scheme (hereinafter, referred to as a TDMA scheme). Use of the CDMA scheme also provides for a greater security of information, and permits recurrent use of frequency bands by allowing a number of terminals to share a broad range of frequency bands. Against such a background, research efforts are directed to a practical application of various schemes.
In mobile communication, a large portion of investment is generally directed to radio-communication stations and equipment for facilitating communication with switch systems. A mobile communication service is generally required to service a large number of terminals where these terminals are spread across a large geographical area, and have a drifting location thereof. Under such conditions, a newly installed mobile communication system is often used together with existing systems which have been in operation before the installation of the new system.
In areas where traffic is relatively small (such areas are hereinafter called non-urban areas), however, it is not justifiable to run a plurality of systems of different schemes when considering costs and other factors. In such areas, unlike in urban areas, only a new system, once installed, is generally allowed to run.
In surroundings as described above, a subscriber needs a dual-mode terminal device which is applicable to any one of the CDMA scheme, the FDMA scheme, and the TDMA scheme if the subscriber desires communication service in both the urban areas and the non-urban areas. Such dual-mode terminal devices are now gradually becoming available in the market, and are directed to combinations of major communication schemes.
FIG. 1 is a block diagram showing a configuration of a dual-mode-terminal device used in the related art.
In FIG. 1, the power-supply node of an antenna 71 is connected to an antenna node of the air-cable sharing device 72, and the air-cable sharing device 72 has a receiver output thereof supplied to a signal input of a DSP (digital signal processor) 77 via a high-frequency amplifier 73, a frequency converter 74, a middle-frequency amplifier 75, and an orthogonal demodulator 76 arranged in a series.
A signal output of the DSP 77 is supplied to a transmitter side of the air-cable sharing device 72 via a orthogonal modulator 78, a middle-frequency amplifier 79, a frequency converter 80, a frequency-band amplifier 81, and a power amplifier 82 connected in a series. A processor 83 has a first output port thereof connected to a control input of a synthesizer 84. The synthesizer 84 has two outputs which are respectively supplied to the frequency converters 74 and 80. The processor 83 has second and third output ports connected to control inputs of synthesizers 85-R and 85-T, respectively. Respective outputs of the synthesizers 85-R and 85-T are supplied to the orthogonal demodulators 76 and 78. Fourth and fifth output ports of the processor 83 are respectively connected to the control inputs of the middle-frequency amplifiers 75 and 79. The DSP 77 has an output port thereof connected to the control inputs of the frequency-band amplifier 81 and the power amplifier 82.
The middle-frequency amplifier 75 includes a switch 86-1, band-pass filters 87-F and 87-C, and a switch 86-2. The switch 86-1 receives a signal having a middle-frequency range from the frequency converter 74 directly, or indirectly after appropriate processing is applied to the signal. The band-pass filters 87-F and 87-C are provided along respective paths extending from the switch 86-1. The switch 86-2 connects an output from either the band-pass filter 87-F or 87-C to a subsequent stage. The switches 86-1 and 86-2 have a control input thereof which receives a binary signal from the fourth output port of the processor 83.
In this related-art configuration, the processor 83 instructs the DSP 77 to establish a channel in a radio-communication zone corresponding to the CDMA scheme when the terminal enters an effective range of the radio-communication zone from outside any service area or when the terminal is newly switched on. Further, the processor 83 controls the synthesizers 84, 85-R, and 85-T to generate a respective radio frequency (for example, 980 MHz, 100 MHz, and 150 MHz, respectively), which is appropriate for the established channel utilizing the CDMA scheme. Also, the processor 83 instructs the switches 86-1 and 86-2 to selectively activate a path corresponding to the band-pass filter 87-C.
The frequency converter 74 receives a radio wave from a radio-communication station (not shown) when the radio wave arrives at the antenna 71 and is forwarded via the air-cable sharing device 72 and the high-frequency amplifier 73. The frequency converter 74 generates a middle-frequency-range signal distributed around a frequency of 100 MHz. This signal corresponds to a differential between the received radio wave and a signal generated by the synthesizer 84.
The middle-frequency amplifier 75 amplifies the middle-frequency-range signal by using the band-pass filter 87-C, which has a frequency band corresponding to the band assigned to the CDMA scheme. The orthogonal demodulator 76 applies orthogonal demodulation to the middle-frequency-range signal based on a signal generated by the synthesizer 85-R. As a result, two base-band signals i and q, which are orthogonal to each other, are generated.
The DSP 77 has a build-in firmware, and applies signal processing equivalent to that of a sliding correlator in accordance with instructions given by the processor 83. As part of the process for establishing a channel, under the control of the processor 83, the DSP 77 attempts to establish synchronization between dispersed codes internally generated and a compressed phase differential of the received radio wave.
The processor 83 gives an instruction to start establishing another channel corresponding to another scheme(for example, the FDMA scheme) other than the CDMA scheme when the attempt to establish synchronization fails in view of certain criteria.
Further, an instruction is given to the switches 86-1 and 86-2 to effect amplification of the middle-frequency-range signal of the frequency converter 74 by activating the path corresponding to the band-pass filter 87-F since the band-pass filter 87-F has a frequency band corresponding to the FDMA scheme. Hereinafter, only specifically relevant matters will be described when describing operations relating to the schemes other than the CDMA scheme since such operations have little bearing on the present invention.
If the attempt to establish synchronization succeeds, the DSP 77 notifies the processor 83 of this fact, and attends to a channel-control procedure under the guidance of the processor 83. During this procedure, various processes are performed with regard to registration of a location, entry into the service area, a transition to a waiting status, a response to a received call, a transmission, and modulation/demodulation of transmitted information (including communication signals) in response to an end of the call and hand-over.
The orthogonal modulator 78 receives a signal from the synthesizer 85-T when the synthesizer 85-T generates this signal having a certain frequency (for example, 150 MHz) in accordance with the instruction given by the processor 83, and applies orthogonal modulation to the signal from the synthesizer 85-T based on the two orthogonal base-band signals i and q, thereby generating a dispersed, modulated signal having a distribution thereof around a frequency of 150 MHz. Here, there is an underlying assumption that the base-band signals indicate transmission information to be transmitted to the radio-communication station via a radio-communication path, and are generated when a dispersing process is applied.
The middle-frequency amplifier 79, the frequency converter 80, the frequency-band amplifier 81, and the power amplifier 82 apply respective processes in an order reverse to the order of corresponding processes applied by the high-frequency amplifier 73, the frequency converter 74, and the middle-frequency amplifier 75 as described above. The dispersed, modulated signal goes through these processes to become a transmission signal distributed around a frequency of 830 MHz.
The transmission signal is then transmitted to the radio-communication path via the air-cable sharing device 72 and the antenna 71, and reaches the radio-communication station. In this manner, a full-two-way communication path is established between the terminal and the base office according to the CDMA scheme.
In the related-art example described above, several tens of seconds are needed before the establishment of synchronization. For example, if a correlation calculation takes 20 msec per unit calculation, and a series of dispersed codes is comprised of 32,727 (215xe2x88x921) bits, a maximum time period that may be needed for establishing synchronization is as long as 655 sec. Because of this, an entry into a service area in which the CDMA scheme is employed takes a lengthy time. Also, there is an undesirable delay in attempting to cope with the FDMA scheme or the TDMA scheme. Further, it is highly likely that such an attempt needs to precede a necessary processing for entry into the CDMA-scheme service area.
In order to obviate these problems, various techniques are available, including
1) using the DSP 77 to implement a plurality of sliding correlators operating in parallel with respect to different phases (different offsets), thereby completing the establishment of synchronism within such a time period as dividing the originally required time period by the number of sliding correlators;
2) applying special dispersed codes designed for establishing the synchronism; and
3) applying a series-estimation scheme by use of a tapped delay-line-matched filter.
The technique identified in 2) is likely to suffer a decline in reliability in establishing synchronism since a plurality of peaks can be found in correlation calculations between the special dispersed codes and the offsets. Such a drawback is not desirable despite a reduction in time required for establishing the synchronism.
All of the above-identified techniques result in unduly complex hardware or software (including firmware implemented in the DSP 77), and, also, are subject to restrictions in one form or another regarding power consumption, circuit density, or real-time property. Because of these, it has been difficult to apply these techniques in practice.
Accordingly, there is a need for a multi-mode communication device which can attend to effective and reliable communication control with respect to the CDMA scheme without employing unduly complex hardware.
Accordingly, it is a general object of the present invention to provide a multi-mode communication device which can satisfy the need described above.
It is another and more specific object of the present invention to provide a multi-mode communication device which can attend to effective and reliable communication control with respect to the CDMA scheme without employing unduly complex hardware.
In order to achieve the above objects according to the present invention, a multi-mode communication device includes a receiving unit which receives a radio signal via a radio communication path, and processes the received radio signal, a frequency-component obtaining unit which obtains frequency components in all or part of a frequency range of the received radio signal, and a controlling unit which selects a multiplex-attachment scheme appropriate for the received radio signal from a plurality of applicable multiplex-attachment schemes by controlling said receiving unit, said controlling unit selecting a CDMA scheme as the multiplex-attachment scheme when the frequency components obtained by said frequency-component obtaining unit are substantially uniformly distributed.
In the multi-mode communication device described above, the check as to whether the received radio signal complies to the CDMA scheme is made based on the degree to which the frequency spectrum of the received radio signal has a uniform distribution. This configuration, therefore, selects an appropriate multiplex-attachment scheme more efficiently than does the related-art configuration which cannot make a determination as to the check until an attempt to establish synchronization is finished.
According to one aspect of the present invention, the multi-mode communication device described above is such that said frequency-component obtaining unit includes a plurality of filters having frequency bands in a frequency range corresponding to the CDMA scheme such that at least one of the frequency bands and band widths thereof are different from each other, and passes the received radio signal through said plurality of filters to obtain levels of the frequency components, and wherein said controlling unit checks whether to select the CDMA scheme based on whether ratios of the respective levels of the frequency components to the band widths of the corresponding filters are substantially the same within a predetermined tolerable range.
In the device described above, the plurality of filters of which at least one of the frequency bands and the band widths is different from each other is used for checking whether the frequency spectrum of the received radio signal has a uniform distribution. The larger the number of the filters and the more uniform a distribution of the respective frequency bands within the frequency range corresponding to the CDMA scheme, the more reliable the check as to whether the CDMA scheme is an appropriate multiplex-attachment scheme.
According to another aspect of the present invention, the multi-mode communication device described above is such that all or part of said plurality of filters have a respective band width that is not equal to a multiple of a frequency interval at which radio frequencies are allocated in a multiplex-attachment scheme that is not the CDMA scheme.
In the device described above, when the received radio signal complies to a multiplex-attachment scheme that is not the CDMA scheme, either some radio frequencies are not covered but side bands thereof are covered or some radio frequencies are covered but side bands thereof are not covered. In the case of the multiplex-attachment scheme that is not the CDMA scheme, therefore, the fact that the distribution of the frequency spectrum of the side bands is not uniform is positively utilized, thereby enhancing the reliability of the check in discriminating the CDMA scheme from another multiplex-attachment scheme.
According to another aspect of the present invention, the multi-mode communication device described above is such that all or part of said plurality of filters have a respective band width in which a number of first radio frequencies allocated to a given zone is different from a number of second radio frequencies not allocated to the given zone when the first and second radio frequencies together constitute a frequency arrangement of a multiplex-attachment scheme that is not the CDMA scheme.
In the device described above, when the received radio signal complies to a multiplex-attachment scheme that is not the CDMA scheme, a proportion of frequency components does not stay constant with respect to the side bands. Therefore, the fact that the distribution of the frequency spectrum of the side bands is not uniform is positively utilized, thereby enhancing the reliability of the check in discriminating the CDMA scheme from another multiplex-attachment scheme.
According to another aspect of the present invention, the multi-mode communication device described above is such that all or part of said plurality of filters have a respective band width which covers side bands of radio frequencies used by a multiplex-attachment scheme that is not the CDMA scheme, but does not cover the radio frequencies themselves.
In the device described above, when the received radio signal complies to a multiplex-attachment scheme that is not the CDMA scheme, only the side-band frequency components which do not have a uniform distribution are covered. Therefore, the check for discriminating the CDMA scheme from another multiplex-attachment scheme is reliably made since the CDMA scheme generally has a uniform distribution of frequency spectrum within a range it occupies.
According to another aspect of the present invention, the multi-mode communication device described above is such that the frequency bands of said plurality of filters together cover an entirety of frequency range which is shared by said plurality of applicable multiplex-attachment schemes.
In the device described above, when the received radio signal complies to the CDMA scheme, the check is made with respect to the entirety of the frequency range that the CDMA scheme occupies. Reliability of the check is thus enhanced compared to when the check is performed only with respect to a portion of the frequency range.
According to another aspect of the present invention, the multi-mode communication device described above is such that all or part of said plurality of filters are used in establishing synchronism for the CDMA scheme.
Since filters of one kind or another are necessary for establishing synchronism for the CDMA scheme even in the related-art configuration, the device described above can minimize the amount of additional hardware by utilizing the same filters for the different purposes. Therefore, consideration for cost, power consumption, a mechanical size, thermal design, etc., does not impose much restriction.
According to one aspect of the present invention, the multi-mode communication device described at the beginning is such that said frequency-component obtaining unit includes at least one filter, of which at least one of a frequency band and a band width is variable, and passes the received radio signal through said at least one filter, and wherein said controlling unit changes at least one of the frequency band and the band width of said at least one filter within a frequency range corresponding to the CDMA scheme to obtain respective levels of the frequency components, and checks whether to select the CDMA scheme based on whether the respective levels of the frequency components indicate a substantially uniform distribution of the frequency components.
In the device described above, the at least one filter of which at least one of the frequency band and the band width is different from each other is used for checking whether the frequency spectrum of the received radio signal has a uniform distribution. The larger the number of the varied frequency bands and the more uniform a distribution of the varied frequency bands within the frequency range corresponding to the CDMA scheme, the more reliable the check as to whether the CDMA scheme is an appropriate multiplex-attachment scheme.
According to another aspect of the present invention, the multi-mode communication device described above is such that said controlling unit sets the band width of said at least one filter to be not equal to a multiple of a frequency interval at which radio frequencies are allocated in a multiplex-attachment scheme that is not the CDMA scheme.
In the device described above, when the received radio signal complies to a multiplex-attachment scheme that is not the CDMA scheme, either some radio frequencies are not covered but side bands thereof are covered or some radio frequencies are covered but side bands thereof are not covered. In the case of the multiplex-attachment scheme that is not the CDMA scheme, therefore, the fact that the distribution of the frequency spectrum of the side bands is not uniform is positively utilized, thereby enhancing the reliability of the check in discriminating the CDMA scheme from another multiplex-attachment scheme.
According to another aspect of the present invention, the multi-mode communication device described above is such that said controlling unit sets the band width of said at least one filter to such a band width in which a number of first radio frequencies allocated to a given zone is different from a number of second radio frequencies not allocated to the given zone when the first and second radio frequencies together constitute a frequency arrangement of a multiplex-attachment scheme that is not the CDMA scheme.
In the device described above, when the received radio signal complies to a multiplex-attachment scheme that is not the CDMA scheme, a proportion of frequency components does not stay constant with respect to the side bands. Therefore, the fact that the distribution of the frequency spectrum of the side bands is not uniform is positively utilized, thereby enhancing the reliability of the check in discriminating the CDMA scheme from another multiplex-attachment scheme.
According to another aspect of the present invention, the multi-mode communication device described above is such that said controlling unit sets the band width of said at least one filter such that the band width covers side bands of radio frequencies used by a multiplex-attachment scheme that is not the CDMA scheme, but does not cover the radio frequencies themselves.
In the device described above, when the received radio signal complies to a multiplex-attachment scheme that is not the CDMA scheme, only the side-band frequency components which do not have a uniform distribution are covered. Therefore, the check for discriminating the CDMA scheme from another multiplex-attachment scheme is reliably made since the CDMA scheme generally has a uniform distribution of frequency spectrum within a range it occupies.
According to another aspect of the present invention, the multi-mode communication device described above is such that said controlling unit changes at least one of the frequency band and the band width of said at least one filter so as to cover in effect an entirety of a frequency range which is shared by said plurality of applicable multiplex-attachment schemes.
In the device described above, when the received radio signal complies to the CDMA scheme, the check is made with respect to the entirety of the frequency range that the CDMA scheme occupies. Reliability of the check is thus enhanced compared to when the check is performed only with respect to a portion of the frequency range.
According to another aspect of the present invention, the multi-mode communication device described above is such that said at least one filter is used in establishing synchronism for the CDMA scheme.
Since filters of one kind or another are necessary for establishing synchronism for the CDMA scheme even in the related-art configuration, the device described above can minimize the amount of additional hardware by utilizing the same filters for the different purposes. Therefore, consideration for cost, power consumption, a mechanical size, thermal design, etc., does not impose much restriction.
Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.